Four poultry workers in Colorado have been diagnosed with bird flu, as confirmed by health officials on Sunday.

These new cases bring the total number in the U.S. to nine since the first human case of the current outbreak was detected in 2022, which also involved a Colorado poultry worker. Of these nine cases, eight have been reported this year alone.

The symptoms observed among the affected workers were relatively mild, including reddened and irritated eyes, along with typical respiratory infection symptoms such as fever, chills, coughing, sore throat, and runny nose. Fortunately, none of the individuals required hospitalization, mirroring the mild nature of other reported U.S. cases.

An additional fifth person displaying symptoms is currently undergoing testing, pending results, according to officials. The affected workers were engaged in culling poultry at a farm in northeast Colorado and had direct contact with infected birds, as confirmed by state health authorities.

Since 2020, a bird flu virus known as H5N1 has been spreading among mammals globally, affecting various species including dogs, cats, skunks, bears, seals, and porpoises. Earlier this year, H5N1 was detected in U.S. livestock and is currently circulating among cattle in multiple states.

Health officials stress that the risk to the general public remains low, emphasizing that the virus has not demonstrated the capability for human-to-human transmission. Nevertheless, vigilance is paramount due to the virus's historical severity in previous strains.

In response to the situation, the Centers for Disease Control and Prevention (CDC) has deployed a nine-person team to Colorado at the state's request to assist in the investigation.

Previous cases earlier this year were reported among dairy farm workers in Michigan, Texas, and Colorado. Genetic analysis indicates that the virus identified in the latest Colorado cases shares at least partial genetic identity with the strains detected in earlier U.S. cases, with ongoing genetic studies aimed at confirming exact similarities.

As of Friday, the U.S. Department of Agriculture has confirmed H5N1 in 152 dairy herds across 12 states. Additionally, hundreds of commercial poultry flocks in over 30 states have reported cases of H5N1 or other strains of bird flu, underscoring the widespread nature of the current outbreak.